Electronic ceramic packages basically comprise laminated layers with conductors on and through one or more major surfaces of each layer. The layers are bonded together by applying heat and pressure. For some applications, one or more central cavities are formed. These cavities are stair-case shaped and formed for receiving a semiconductor chip which is bonded and electrically connected to metal pads which are exposed on the various layers or steps of the stair-case. Often the package is subsequently attached to a standard printed wiring board that contains other components.
One of the problems associated with fabricating this structure involves the bending and deformation of wire bonding pads during the bonding process. Deformed and distorted wire bonding pads are not suitable for automated wire bonding.
Another problem associated with fabricating this type of structure involves delamination of the various layers. Multilayer packages containing cavities for receiving semiconductor chips often require multiple pressings, usually three or four pressings, to laminate the stairs within the cavity. The pressings are typically performed between rigid platens of a parallel platen press. Parallel platens require multiple pressings because they cannot simultaneously press the top, bottom and horizontal surfaces within the cavity.
However, the cross sectional thickness of the layers varies considerably from end to end. This is the result, in part, of patterns of electrically conductive paste that are formed on at least some of the layers. The conductive paste forms the internal electrical pathways of the final package. When pressed between parallel rigid platens, the nonuniformity of the thickness of the stack causes local variations in the pressure across the stack's surface. Pressure variations are undesirable in that they can distort the package beyond acceptable dimensional tolerances and/or result in poor lamination.
In addition, fabricating practices that require multiple pressings are inefficient. In general, they increase both the operating expense and capital expenditures.
U.S. Pat. No. 4,636,275 to Norell discloses an elastic bladder method of fabricating an integrated circuit package having bonding pads in a stepped cavity. The patent teaches a method which includes the use of a bladder which fills with fluid during the lamination process to match the shape of the cavity and prevent the flow of interlayer adhesive, integral to this process.
U.S. Pat. No. 4,680,075 to McNeal et al discloses a thermoplastic plug method of fabricating an integrated circuit package having bonding pads in a stepped cavity. The patent teaches a method in which a preformed thermoplastic plug which has a shape that closely matches the shape of the cavity is used to prevent adhesive between layers from flowing out of the stack of sheets onto bonding pads on the steps of the stair-case cavity. The McNeal et al process require the fabrication of new plugs and such fabrication of new plugs is time consuming and expensive. In addition, production costs increase due to the time required to install the plug and remove the plug after lamination.
U.S. Pat. No. 4,737,208 issued to Blochle et al discloses a method of fabricating multilayer structures with nonplanar surfaces. A conformable material, a release material, and an optional template are provided over the structure prior to the lamination bonding operation. The conformal and release materials then fill the cavity during the bonding operation to prevent flow of adhesive from between the layers into the cavity, and the template redistributes cavity edge stresses to minimize deflection of the wire bonding pads. The conformal and release materials are then discarded. The template can be reused.
It is, therefore, a primary objective of the invention is to provide a method of manufacturing multiple layer structures with cavities therein so as to maximize product quality and minimize manufacturing costs.
Another objective of the invention is to provide a method of manufacturing multiple layer structures with cavities capable of decreasing defects resulting from nonuniform application of pressure during lamination.
Another objective of the invention to is provide a method of manufacturing multiple layer structures with cavities that can be laminated in a single pressing.
Yet another objective of the invention is to provide a method of manufacturing multiple layer structures with cavities therein so as to prevent the bending and distortion of wire bonding pads that can interfere with automated wire bonding.
Still another objective of the invention to provide a method of manufacturing multiple layer structures with cavities that can be repeatedly practiced without the need to change conformal material that is being used in the press operation.
These and other objectives and advantages of the present invention will be more fully understood and appreciated with reference to the following description.